1. Field of the Invention
The present invention relates to a method and apparatus for treating waste gas and in particular to a method and apparatus for treating waste gas containing PFC and/or HFC.
2. Description of the Related Art
In perfluorinated compound (PFC) waste reduction technology, process modification, such as promoting the utilization efficiencies of perfluorinated compounds in the process and using substitutes for perfluorinated compounds, recover and reuse, and end-of-pipe treatment are commonly used. Although end-of-pipe treatment is not the best choice for waste reduction, it is the most mature, economical, and efficient way to reduce perfluorinated compounds and/or hydrofluorocarbons (HFCs). Among the various end-of-pipe treatment methods, the combustion-based decomposition process is a well-developed PFC treatment technology, which uses a combustion temperature higher than 1200° C. The catalytic combustion-based decomposition process treats PFCs with catalysts at a relatively low temperature between about 500° C. and 750° C. The plasma-based process utilizes a localized, relatively high temperature to treat PFC and the central temperature may exceed than 3000° C. These methods consume an excessive amount of energy and pose a high risk of fire.
U.S. patent application Ser. No. 20020150527 and WO 01/21304 A1 disclose a catalyst composition and a treatment method wherein PFC and HFC are decomposed using the catalyst composition. The catalyst composition includes aluminum oxide preferably stabilized by the addition of, for example, titanium, zirconium, cobalt, compounds thereof, or mixtures thereof. The operating temperature must be higher than 300° C., and preferably from about 500° C. to 800° C., without the use of ozone and iron oxide.
Among transitional metal oxides, ferric oxide has moderate oxidation reactivity respective to H2, CO, CH4, and paraffin. The examples of transitional metal oxides as catalysts are mainly seen in applications for oxidation, hydrogenation, or dehydrogenation. Ferric oxide is commonly used as a catalyst in, for example, high temperature conversion reaction, synthesis reaction of polystyrene from styrene, ammonia synthesis reaction, and reaction for removal of hydrogen sulfide.
Ozone is a very strong oxidant and widely used in water treatment, organic synthesis, and food sanitizing. Upon the decomposition of the pollutant by ozone, the ozone is immediately reduced to molecular oxygen without generating residue or causing secondary pollution.
Nevertheless, iron oxide and ozone have never been used in combination for treating PFCs and HFCs.
In view of the United Nations Framework Convention on Climate Change and Kyoto Protocol, and the parties agreeing to the Protocol, the emissions of greenhouse gas (including PFCs and HFCs) are to be further restricted between 2008 and 2012 to protect the environment. Hence, there is a need for a better method and apparatus for treating waste gas containing PFC and/or HFC.